A significant problem in the construction of rail systems is the joining of individual rails to form a track. A traditional method of joining rails in linear alignment is depicted in FIGS. 1(A) and 1(B). Such joining has involved the positioning of two rails 30 and 32 in linear alignment with their ends 34 and 36 abutting one another. A gap 38 is disposed between the two ends 34 and 36 that allows for thermal expansion. Such expansion may be significant in regions where large temperature changes occur over the course of the year. The two rails are maintained in alignment by means of a pair of splice plates 40 bolted through the sides of the rail and resting upon the upright rail web 42. Note that the splice plates include slots 44 to allow for displacement of the rails relative to the plates due to thermal expansion and contraction.
The joined rail unit is also secured to a tie 46 using a set of spikes 48 driven therethrough that hold the rail flush against an aligning spike plate 50 disposed between the rail base 52 and the tie surface. The figures also illustrate a traditional metallic railroad wheel 54 having a rolling surface 56 that contacts the rail top surface and a guiding flange 58 that contacts the inner facing side of the rail. This wheel must travel over countless numbers of joints having gaps 38 as it travels from one point to another and this gap traversal may cause problems.
A particular problem associated with these gaps is clearly depicted in FIG. 2. Each time a railroad wheel 54 traverses a gap 38 between two rails 30, 32, a discrete arc 60 of the wheel surface drops into the gap 38, falling a distance D below the top surface 62 of the rail. The larger the gap distance G, the greater the drop distance D. One particular problem associated with gaps is the considerable loss of ride smoothness. This smoothness of ride is critical in very high speed train applications. This may be a significant concern in passenger transport, especially in the case of "bullet trains" currently proposed in the U.S. and other countries. Of equal concern in either passenger or especially freight transport is the energy loss resulting from the traversal of gaps. Assuming that each wheel supports at least 5,000 pounds and that each wheel drops 0.010 inches, and that rail gaps are spaced at 125 per mile, then a car with eight wheels in rising back out of each gap will expend energy equivalent to lifting 5,000 pounds approximately ten inches for each mile of horizontal travel. Assuming that a train has at least twenty cars, then the rise will equal 200 inches per mile for every 5,000 pounds carried by the train. Thus, for a large heavy train, the amount of energy expended simply in traversing joint gaps is significant.
In some very temperature stable regions of the country it may be possible to reduce the effect of gaps by joining rail ends closely together. However, wherever any significant degree of temperature change is encountered, sizable joint gaps are necessary for all discrete sections of rail to be joined together. This is because thermal expansion would otherwise deform closely abutting rails. Therefore, one solution to the problem of joint gaps is the elimination of joints themselves through welding of rail ends together or other permanent joining processes. This system has a clear drawback in that it is a fairly expensive process and renders repairs and replacement of rail sections significantly more difficult.